This invention relates to a method for producing a plate or sheet useful in planographic (lithographic) printing. More particularly, the invention relates to a method for producing a plate or sheet useful in planographic printing which comprises an oleophilic body having a hydrophilic layer formed on the surface.
In the conventional art of planographic printing, particularly in the art of offset printing such as for easy business-use, an offset master sheet of low quality prepared by the electrostatic plate making method is well known. For example, a photoconductive layer formed and electrostatically charged on a non-electroconductive substrate is exposed to light for desensitizing of the non-image area and forming a latent image to which an oleophilic material is applied and forms printing elements on the image area by electrostatic force; thus an offset master sheet is obtained.
In the above electro-static plate making method, however, the steps of development and fixing are necessary after the formation of latent image by light exposure, and therefore it is not so convenient. Further, the oleophilic material (the so-called toner) cannot be applied with sufficient selectivity and fineness to the surface of the substrate, so that the resolving power of images is inferior in precise printing.
In consideration of the above-mentioned planographic printing plate, especially of the master sheet for business-use offset printing machines, the inventor has proposed a new printing material which is low in cost, easy in plate making and good in resolving power of printing images. The plate or sheet useful in planographic printing is made by chemically treating the surface of an oleophilic body comprising oleophilic resin to form a hydrophilic layer on the surface (Japanese patent application No. 113,513 of 1972). For all the excellent properties of this material in practical uses, it is disadvantageous that strong oxidizing agents must be employed in the chemical treatment process. That is, it is very troublesome to take charge of the treating agents without the loss of their effect and to treat the waste of used treating agents.